User should be able to set image URL for application #323

Remove image file upload
Add logo_url with validation for 'https' prefix
User should be able to set image URL for application #323

Extend doorkeeper application with logo_url
Remove paperclip fields from db
Add test for logo_url format validation
Feature/logo url #344

Replace domain.com with example.com
Feature/logo url #344

Remove paperclip
Update migrations to handle paperclip fields without using gem
Merge branch 'devel' of github.com:18F/myusa-server into feature/logo_url

Conflicts:
	app/controllers/applications_controller.rb
	db/schema.rb
	lib/doorkeeper_patches/concerns/application_extension.rb
Merge branch 'feature/logo_url' of github.com:18F/myusa-server into feature/mail-branding